Motion capture systems are used in the production of animation to capture the performance of an actor by recording the 3-dimensional (hereinafter, ‘3D’) location of a set of markers placed on the actor, either physically or by software association with identifiable features of the actor's physiognomy.
Motion capture (or, “mocap”) systems use a variety of physical techniques to record the location of the markers, but the output of every system is similar: a set of 3D positions in space for every ‘frame’ captured. For example, a motion capture system might be set up to record the position of 200 key markers on an actor at 30 frames-per-second. This means that a set of 200 3D coordinates is returned by the system 30 times each second.
Usually, the 3D data are passed into some animation software and the movement of the data is translated to the movement of a synthetic character (the animated character).
Motion capture data typically require cleaning both because of measurement inaccuracy and because of the absence or unreliability of data when markers are unobservable due to the orientation of the subject or masking by another object in the frame. However, the effort required to clean motion capture data may be as extensive, in some cases, as the effort to create animation from scratch.
The ‘raw’ data returned by motion capture systems is often corrupted. The data can be both ‘noisy’ and ‘incomplete’. To cite one example, a motion capture system may be used to track markers attached to an actors face. Errors and inaccuracy in the physical system dictate that there will typically be inaccuracy in the returned 3D location of each points. Over the sequence, the returned data points may appear to ‘jitter’ due to measurement inaccuracy. On some occasions, the coordinates of a 3D location for a particular point may be missing entirely from a frame.
On other occasions an even bigger problem can occur: the markers on the actor may be unreadable (for example, a prop, say a mug, comes between the markers and the capture system). Under these circumstances, the 3D locations of a significant number of points may be missing from one or more frames.
Ideally, a motion capture would return a set of 3D points for every point on the actor, for every frame. However, in reality, at each frame there are often one or more missing points, which make the data difficult to use by animators. Moreover, even when data points are present, there may be significant error in the values returned describing their 3D position.
It is thus desirable that a method be provided for robust and efficient cleaning of mocap data.